Occurrence of different species of fusarium from wheat in relation to disease levels predicted by a weather-based model in Argentina pampas region.

Fusarium head blight (FHB) is an important disease throughout many of the world wheat-growing areas that have humid to semi-humid climate. The infection happens mainly during the anthesis of the wheat, when there have been favorable conditions of moisture and temperature. The direct relation of the infection to environmental factors makes possible the formulation of mathematical models that predict the disease. The causal agent of the FHB of the spike of wheat is attributed principally to Fusarium graminearum. High economic losses due yield decrease have been recorded in Argentina. In the present work, 67 isolates of Fusarium spp. were obtained from samples of wheat grains from Pampas region from 15 locations distributed in Buenos Aires, Entre Ríos, Santa Fe and Córboba provinces during 2006 and 2007 wheat-growing seasons. The identification of species from monosporic isolates was carried out by morphological characterization and use of species-specific PCR-based assays. Both identification criteria were necessary and complementary for the species determination, since in some cases the molecular identification was not specific. Scanty presence of F. graminearum was observed in 2006 wheat-growing season coinciding with the lack of favorable meteorological conditions for producing FHB infection events. High presence of F. graminearum isolates was observed in 2007 wheat-growing season, in accordance with moderate incidence of the disease according to spatial distribution of FHB incidence values. The aim of this report was to identify the causal agent of the FHB disease by different taxonomic criteria and to relate its occurrence with disease incidence values predicted by a weather-based model in Argentina.

Purification and characterization of an extracellular endo-1,4-beta-xylanase from Fusarium oxysporum f. sp. melonis.

Fusarium oxysporum f. sp. melonis produces extracellular endo-1,4-beta-xylanase and beta-xylosidase when grown in shaken culture at 26 degrees C in a mineral salts medium containing oat spelt xylan and glucose as carbon sources. Endo-1,4-beta-xylanase was purified 251 times from 5-day-old culture filtrates, by Sephacryl S-200, ion exchange and gel filtration HPLC. The purified sample yielded a single band in SDS polyacrylamide gels with a molecular mass of 80 kDa on electrophoretic mobility and 83 kDa by gel filtration behavior. High activity of the endo-1,4-beta-xylanase against xylan was observed between 5 and 8 pH, and between 40 and 60 degrees C, the optimum pH and temperature being 5.0 and 50 degrees C, respectively. Kinetic properties of the enzyme are similar to those of other fungal xylanases, showing high affinity towards oat spelt xylan with a Km of 1 mM expressed as xylose equivalent.

[Isolation of protoplasts from vegetable tissues using extracellular lytic enzymes from fusarium oxysporum f.sp. melonis]. / Aislamiento de protoplastos en tejidos vegetales por enzimas líticas extracelulares de Fusarium oxysporum f.sp. melonis.

Fusarium oxysporum f.sp. melonis, a pathogen of melon (Cucumis melo L.), was grown in shaken cultures at 26 degrees C in a mineral salts medium containing glucose, xylan and apple pectin as carbon sources. The extracellular enzymic complex obtained from these cultures showed lytic activity on plant tissues, causing maceration of melon fruits, potato tubers and carrot roots. Protoplasts were isolated from melon fruits when the maceration was carried out under appropriate osmotic conditions. This fact suggest a possible relationship between the enzymes produced by Fusarium oxysporum f.sp. melonis and their pathogenicity on melon plants.

Aislamiento de protoplastos en tejidos vegetales por enzimas líticas extracelulares de Fusarium oxysporum f.sp. melonis / [Isolation of protoplasts from vegetable tissues using extracellular lytic enzymes from fusarium oxysporum f.sp. melonis]

Fusarium oxysporum f.sp. melonis, a pathogen of melon (Cucumis melo L.), was grown in shaken cultures at 26 degrees C in a mineral salts medium containing glucose, xylan and apple pectin as carbon sources. The extracellular enzymic complex obtained from these cultures showed lytic activity on plant tissues, causing maceration of melon fruits, potato tubers and carrot roots. Protoplasts were isolated from melon fruits when the maceration was carried out under appropriate osmotic conditions. This fact suggest a possible relationship between the enzymes produced by Fusarium oxysporum f.sp. melonis and their pathogenicity on melon plants.